Once each tower began to collapse, the weight of all the floors above the collapsed zone bore down with pulverizing force on the highest intact floor. Unable to absorb the massive energy, that floor would fail, transmitting the forces to the floor below, allowing the collapse to progress downward through the building in a chain reaction. Engineers call the process "pancaking," and it does not require an explosion to begin, according to David Biggs, a structural engineer at Ryan-Biggs Associates and a member of the American Society of Civil Engineers (ASCE) team that worked on the FEMA report.

Like all office buildings, the WTC towers contained a huge volume of air. As they pancaked, all that air—along with the concrete and other debris pulverized by the force of the collapse—was ejected with enormous energy. "When you have a significant portion of a floor collapsing, it's going to shoot air and concrete dust out the window," NIST lead investigator Shyam Sunder tells PM. Those clouds of dust may create the impression of a controlled demolition, Sunder adds, "but it is the floor pancaking that leads to that perception."

Demolition expert Romero regrets that his comments to the Albuquerque Journal became fodder for conspiracy theorists. "I was misquoted in saying that I thought it was explosives that brought down the building," he tells PM. "I only said that that's what it looked like."

Romero, who agrees with the scientific conclusion that fire triggered the collapses, demanded a retraction from the Journal. It was printed Sept. 22, 2001. "I felt like my scientific reputation was on the line." But emperors-clothes.com saw something else: "The paymaster of Romero's research institute is the Pentagon. Directly or indirectly, pressure was brought to bear, forcing Romero to retract his original statement." Romero responds: "Conspiracy theorists came out saying that the government got to me. That is the farthest thing from the truth. This has been an albatross around my neck for three years."

Many conspiracy theorists point to FEMA's preliminary report, which said there was relatively light damage to WTC 7 prior to its collapse. With the benefit of more time and resources, NIST researchers now support the working hypothesis that WTC 7 was far more compromised by falling debris than the FEMA report indicated. "The most important thing we found was that there was, in fact, physical damage to the south face of building 7," NIST's Sunder tells PM. "On about a third of the face to the center and to the bottom—approximately 10 stories—about 25 percent of the depth of the building was scooped out." NIST also discovered previously undocumented damage to WTC 7's upper stories and its southwest corner.

NIST investigators believe a combination of intense fire and severe structural damage contributed to the collapse, though assigning the exact proportion requires more research. But NIST's analysis suggests the fall of WTC 7 was an example of "progressive collapse," a process in which the failure of parts of a structure ultimately creates strains that cause the entire building to come down. Videos of the fall of WTC 7 show cracks, or "kinks," in the building's facade just before the two penthouses disappeared into the structure, one after the other. The entire building fell in on itself, with the slumping east side of the structure pulling down the west side in a diagonal collapse.

According to NIST, there was one primary reason for the building's failure: In an unusual design, the columns near the visible kinks were carrying exceptionally large loads, roughly 2000 sq. ft. of floor area for each floor. "What our preliminary analysis has shown is that if you take out just one column on one of the lower floors," Sunder notes, "it could cause a vertical progression of collapse so that the entire section comes down."

There are two other possible contributing factors still under investigation: First, trusses on the fifth and seventh floors were designed to transfer loads from one set of columns to another. With columns on the south face apparently damaged, high stresses would likely have been communicated to columns on the building's other faces, thereby exceeding their load-bearing capacities.

Second, a fifth-floor fire burned for up to 7 hours. "There was no firefighting in WTC 7," Sunder says. Investigators believe the fire was fed by tanks of diesel fuel that many tenants used to run emergency generators. Most tanks throughout the building were fairly small, but a generator on the fifth floor was connected to a large tank in the basement via a pressurized line. Says Sunder: "Our current working hypothesis is that this pressurized line was supplying fuel [to the fire] for a long period of time."

WTC 7 might have withstood the physical damage it received, or the fire that burned for hours, but those combined factors—along with the building's unusual construction—were enough to set off the chain-reaction collapse.

I have repeatedly stated many times over. The events of September was staged. It was all theater and orchestrated by other than your friendly American government. Whether they will deny it, or even admit partial...the truth will be buried along with the JFK and the Pearl Harbor conspiracies.

We the American People, knows what really happened on that warm and sunny Tuesday morning of September 11th, 2001. We aren't as stupid as the government makes us out to be. Right?

I have repeatedly stated many times over. The events of September was staged. It was all theater and orchestrated by other than your friendly American government. Whether they will deny it, or even admit partial...the truth will be buried along with the JFK and the Pearl Harbor conspiracies.

We the American People, knows what really happened on that warm and sunny Tuesday morning of September 11th, 2001. We aren't as stupid as the government makes us out to be. Right?

You may state it as many times as you like, that does not make it true.

Why the hell are you on a conspiracy forum and siding with the government's account of the 911 terrorist attack?

I am here to inform you that you should remove yourself from CC and join the government at their forums.

Interesting that the 911 terrorists knew exactly where to crash the planes into the towers in order to make the buidings collapse.

Or, should we believe that they had no clue and the buildings came crumbling down due to other forces?

It should be fairly obviously why I'm posting on a conspiracy forum. For those that missed it, let me break it down.

Someone posted a video with the same outlandish claims that have been debunked time and time again. I responded to that video by providing explanations and answers to the "questions" the subject of the video had.

I have no idea if they knew exactly where to crash the plans to destroy the buildings. Do you have direct knowledge that the terrorists knew exactly where to impact?

Using their history of attacks worldwide, I would say it's a logical assumption that the collapse was some what of a coincidence.

If you feel it possible for the government to produce such an elaborate hoax, and keep it relatively hidden, why is it so hard to believe that a terrorist network could use readily available information on the internet, specialized education programs, and so called "sleeper agents" to launch such an attack?

Asking questions is great. Dismissing answers because they don't line up with what you believe is not.

Can a person spew as much BS as you have right now? (meant for Brice, the expert?)
Yes they can, exeptions like Obama Bin Bush.
You should enroll as a comedian, you'd have more luck there.
Because right now im laughing at you

Can a person spew as much BS as you have right now? (meant for Brice, the expert?)
Yes they can, exeptions like Obama Bin Bush.
You should enroll as a comedian, you'd have more luck there.
Because right now im laughing at you

I never claimed to be an expert about September 11th conspiracy theories or anything else. I do, however, rely on other experts who are studied and knowledgable in their field.

I'm glad that's laughable for you. Instead of laughing, and attacking me personally, you should try to produce some substantial and verifiable evidence to contradict any of the statements I made.

And no, your statement, or the statements of any other nutjobs on youtube or wikipedia, probably does not constitute substantial or verifiable evidence.

You may believe something all you like, even when it flies in the face of logic and common sense, but that does not make it true.

It's not me, just me, lol, where the hell have you been, under a rock?
The World knows the truth. Dont underestimate people.
Never underestimate the human spirit and it's determination for truth.
Now why would I waste my personal time to counter the manure that you have dropped? I know the truth, so do most of the members here, deal with it

You may state it as many times as you like, that does not make it true.

Hmmm....so you seriously think, in your own mind. And, not in another person's opinion, it was just a coincidence?

If you know your American history, you have to go far as back as the Cuban Missile Crisis in the 1960's. Honestly, even though, both Russia and the United States were fighting for Supremacy for being the "Superpowers" of the world, there was also a man name Bin Laden, whom we are all now familiar with. I am sure, if 9/11 didn't ever happen, this man would not be a household name.

I never claimed to be an expert about September 11th conspiracy theories or anything else. I do, however, rely on other experts who are studied and knowledgable in their field.

I'm glad that's laughable for you. Instead of laughing, and attacking me personally, you should try to produce some substantial and verifiable evidence to contradict any of the statements I made.

And no, your statement, or the statements of any other nutjobs on youtube or wikipedia, probably does not constitute substantial or verifiable evidence.

You may believe something all you like, even when it flies in the face of logic and common sense, but that does not make it true.

You cannot truly rely on those sources (i.e. Youtube, Leakipedia, and other news sources). They are there simply to manipulate you to believe otherwise. You have to go straight to the source. The people that were involved. Of course, none of us have spoken directly to those who were involved. Because, they will "deny" all they want. And, trying to get the truth out of them, is like picking teeth from a gay goat.